1. Field of the Invention
This invention relates generally to sealing devices for providing a close seal between a stationary member and a member pivotal in relation thereto and, more particularly, with respect to aircraft gas turbine engines, between engine ducts and outer flaps of vectorable or non-vectorable exhaust nozzles.
2. Discussion of the Background Art
Exhaust nozzles for military aircraft gas turbine engines typically include outer flaps which define the outer wetted surface of exhaust nozzle and is exposed to the airstream flowing past the aircraft. The outer flaps are usually hinged to an outer engine casing. Typical types of exhaust nozzles include axisymmetrical vectorable and nonvectorable and two dimensional. Vectorable nozzles generally employ divergent flaps to turn or vector the exhaust flow and thrust of the gas turbine engine powering the aircraft. Two dimensional nozzles have been devised which employ relatively flat flaps to direct the pitch or yaw direction of the engine's thrust. Hauer, in U.S. Pat. No. 4,994,660 incorporated herein by reference, discloses an Axisymmetric Vectoring Nozzle (i.e., General Electric's AVEN.RTM. nozzle) that provides a means for vectoring the thrust of an axisymmetric convergent/divergent nozzle by universally pivoting the divergent flaps of the nozzle in an asymmetric fashion or in other words pivoting the divergent flaps in radial and tangential directions with respect to the unvectored nozzle centerline. Wood et al., in U.S. Pat. No. 5,485,959 incorporated herein by reference, discloses a thermal shield for the Axisymmetric Vectoring Nozzle with outer flaps and seals.
Hot pressurized nozzle flow is contained by convergent and divergent flaps and seals (in the case of axisymmetric nozzles) wherein the divergent flaps and seals are pivotally connected to the nozzle throat in a manner permitting pivotal movement and axial translation of the exhaust nozzle exit. Outer flaps pivotally connected to an exhaust casing of the engine and outer seals (when used) supported by and disposed the outer flaps are used to surround the nozzle's convergent and divergent flaps and seals as demonstrated in U.S. Pat. No. 4,128,208 by Ryan et al., entitled "Exhaust Nozzle Flap Seal Arrangement" assigned to the same assignee as the present invention. The outer flaps and seals are convergent in shape in the aft direction and are designed to provide an aerodynamically smooth surface around the nozzle to prevent adverse aerodynamic conditions that might otherwise arise. Because of the convergent shape, airflow along the outer flaps and seals are prone to separation which causes a highly undesirable increase in boat-tail drag on the nozzle, engine and ultimately the aircraft. Therefore, it is highly desirable to forestall separation as far aft on the outer flaps as possible and to eliminate separation along the flaps, if possible.
The hot pressurized nozzle flow tends to leak out of the nozzle flow path and into a nozzle bay formed between the convergent and divergent flaps and seals and the outer flaps. This pressurizes the bay which then leaks relatively high pressure airflow between the engine casing and the outer flaps and seals where the outer flaps are pivotally connected to the exhaust casing of the engine by hinges. The leakage from the bay can cause the boundary layer along the outer flaps and seals to trip from laminar to turbulent flow and, in turn, to cause the airflow along the outer flaps and seals to separate, thus, bringing about the unwanted increase in boat-tail drag. The separation can cause other undesirable effects relating to aerodynamic flow instabilities caused by the flow separation. U.S. Pat. No. 4,022,948 discloses resiliently coated metallic finger seals having two overlapping metallic seal members fixed at one set of ends with fingers extending backward at another set of ends encapsulated with resilient coating material. The slits between the fingers are offset between fingers so that resilient coating material cannot extend continuously between coatings over the upper and lower fingers. The resilient coating extends almost to the end of the slits but doesn't form an elastic seal entirely around the fingers. The problem of leakage is compounded by the strong aerodynamic forces acting along the interface between the engine casing and the outer flaps and seals and because the outer flaps and seals are pivoted with respect the engine casing.
The present invention overcomes these problems by providing an elastic seal which functions like a rubber band to keep the elastic seal tightly but resiliently against sealed elements. The elastic seal has at least one embodiment that can be used between the engine casing and the outer flaps and seals and which can be used for axisymmetric vectoring and non-vectoring nozzles and for two dimensional vectoring and non-vectoring nozzles. These features and advantages will become more readily apparent in the following description when taken in conjunction with the appended drawings.